It's all part of the fight-or-flight response, which uses adrenaline to prime the human body for for stressful situations. In fact. the body reacts to danger on a sliding scale, though, so the stresses of a job interview illicit similar—but less severe—reactions to, say, a shark attack. This video explains how those nervous feelings come about—including the way redirection of blood from your stomach makes it feel all... funny. [ASAP Science]